catch all 250 pokemon and go to prof elm and he will give you a gs ball
Legendary dogs Capture-
use max/super repel on the area and get a pokemon with mean look (golbat,gastly,haunter).equiped with quick claw and use mean look on the dogs and use fast/ultra/master balls to capture.
Legendary dogs hideout(i think!)-
suicine-below eucreak city (sometimes)
entei-below blackthorn city
raikou-the left of eurcteak city